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Il progetto definitivo della Gronda di Genova

Selleri Alberto Mazza Orlando
Articolo Immagine
ISSN:
0393-1641
Rivista:
Gallerie e grandi opere sotterranee
Anno:
2013
Numero:
106
Fascicolo:
Gallerie e grandi opere sotterranee n.106/2013

L’articolo riporta un inquadramento generale delle opere in sotterraneo previste nell’ambito della Gronda di Genova, illustrandone il contesto geologico, le caratteristiche geometriche e le modalità di scavo. Considerata la complessità dell’opera, un vero e proprio green field urbano, si è privilegiata l’illustrazione - nontanto degli aspetti squisitamente tecnici relativi allo scavo  delle gallerie - quanto della serie di problematiche di contorno di tipo autorizzativo (il Dibattito Pubblico),ambientale (in particolare il tema della gestione della problematica “amianto”),idrogeologico e logistico (il trasporto dello smarino con lo slurrydotto, i cantieri e leviabilità di servizio) oltre agli aspetti relativi alla sicurezza in fase di esercizio.Opera ingegneristica di assoluta importanza a corollario della Gronda è l’Opera a Mare realizzata con lo smarino delle gallerie, che prevede la posa di oltre 4.000 ml dicassoni cellulari in c.a. con altezze dell’ordine di 15 ml.

The “Gronda di Genova” final project.

The “Gronda di Genova” is a new motorway with two lanes for direction that will double the existing A10 Genoa – Savona motorwaypassing through the city of Genoa,upgrading the lines of A7 and A12 located between the existing tolling plaza of Genoa East, Genoa West and Bolzaneto. The peculiar morphology of the territory where the new infrastructure will be built has led to anintensive use of the subsoil. The new motorway system will develop almost entirely underground and will include 25 tunnels fora total of 50 Kilometres of underground route, with sections ranging from 12 squaremetres diameter of the emergency tunnel,to 200 square metres of the TBMs thatwill double the A10, until the 500 squaremetres of the interconnection large tunnelsbetween two motorway lines.During the execution of works, massiverocks will be excavated for more than 9 million of cubic metres; 50% of excavate drocks might contain asbestos fibres. The layoutWhat the underground works concerns, we can identify 3 areas: Voltri, Varenna and Polcevera. The voltri area In the Voltri area, three double bored motorway tunnels will be built on the main route: Borgonuovo East (2223 metres); Borgonuovo West (2243 metres); Voltri West (284 metres); Voltri East (261metres); Amandola East (5994 metres);Amandola West (6014 metres) and other single tunnels at the level of the interchange lanes: Ciocia (460 metres); Bric del Carmo (895 metres); Delle Grazie(1305 metres). The East and West Voltri, Ciocia, Bric del Carmo e delle Grazie tunnels, although interested by a geological structure probably containing asbestos, because of their reduced length, section variability and the tortuous path, will be realized with traditional excavation techniques. The Varenna Area The tunnels that will be built in the VarennaArea, Amandola West (6014 metres) and East (5994 metres) and Monterosso West(6230 metres) and East (6228 metres) willbe excavated with two tunnel boring machines. The excavation works, the lining of the tunnel,and transport of the excavated materialwill be managed, for all the tunnel sequence,from a single entrance work sitewhich is located in the Polcevera valley inBolzaneto.This reduces consistently the constructionworks on the surface in Varenna and VoltriValleys.The Polcevera AreaThe motorway line on the right side ofthe Polcevera River, develops exclusivelyunderground. The construction of the followingtunnels is expected: Morego (158metres); Polcevera (575 metres); Baccan(1578 metres); San Rocco (1276 metres);Forte Diamante (2810 metres); Bric duVento (2507 metres); Torbella West (398metres); Torbella East (136 metres); MonteSperone (1978 metres) Forte Begano(1386 metre) Granarolo (3.368 metres);Moro 1 (886 metres); Moro 2 (796 metres); Campursone (142 metres). In this area, the presence of several interchangelanes, connecting to the principalroute, produces underground connections,with very large excavation sections called“caverns”.Tunnels and excavation sectionsThe 14 tunnels on the east side of thePolcevera river, considering the variabilityof sections and the several undergroundconnections, will be bored with traditionalexcavations technologies (drill and blast orhammer).6 out of 11 tunnels located on the westside of the Polcevera river, will be excavatedwith mechanized system with TBMs: theseare double bored tunnels on the motorwaymain route (Monterosso, Amandola e Borgonuovo) that mainta in the same sectionand show relevant lengths (6 km forthe Monterosso and Amandola tunnelsand about 2,2 km for the Borgonuovotunnels) The remaining 5 tunnels on the west side of the Polcevera River, will be built with traditional excavation techniques because of the limited length or the variability of the sections.Interconnections “caverns”The several tunnels included in the project have required the realization of intersection areas (the so called “caverns”) in the sections where the rocks show the best geomechani calconditions. The excavation method used for the cavernsis the traditional one (drill and blastor hydraulic hammer). According to the geomechanical conditions, within the final project, a construction based on the sequential excavation method has been developed.This method is able to guarantee the necessary safety level, either during the construction or in the operating time of the infrastructure, reconciling the operational needs of the work site with the maintenance of a safe work environment during the excavationphase.

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